import math

a = int(input(':'))
b = int(input(':'))
c = int(input(':'))

p = (a+b+c) / 2

if a+b>c and a+c>b and b+c>a:
    s = p*(p-a)*(p-b)*(p-c)
else:
    print('这三个数无法组成三角形。')
    s = 0

a = math.sqrt(s)

print(a)